1. Field of the Invention
The present invention relates to an apparatus and method for detecting the presence, amount, or rate of binding of one or more analytes in a sample, and in particular, to apparatus and method based on fiber optic interferometry.
2. Description of the Related Art
Diagnostic tests based on a binding event between members of an analyte-anti-analyte binding pair are widely used in medical, veterinary, agricultural and research applications. Typically, such methods are employed to detect the presence or amount or an analyte in a sample, and/or the rate of binding of the analyte to the anti-analyte. Typical analyte-anti-analyte pairs include complementary strands of nucleic acids, antigen-antibody pairs, and receptor-receptor binding agent, where the analyte can be either member of the pair, and the anti-analyte molecule, the opposite member.
Diagnostics methods of this type often employ a solid surface having immobilized anti-analyte molecules to which sample analyte molecules will bind specifically and with high affinity at a defined detection zone. In this type of assay, known as a solid-phase assay, the solid surface is exposed to the sample under conditions that promote analyte binding to immobilized anti-analyte molecules. The binding event can be detected directly, e.g., by a change in the mass, reflectivity, thickness, color or other characteristic indicative of a binding event. Where the analyte is pre-labeled, e.g., with a chromophore, or fluorescent or radiolabel, the binding event is detectable by the presence and/or amount of detectable label at the detection zone. Alternatively, the analyte can be labeled after it is bound at the detection zone, e.g., with a secondary, fluorescent-labeled anti-analyte antibody.
Co-owned U.S. Pat. No. 5,804,453, (the '453 patent) which is incorporated herein by reference, discloses a fiber-optic interferometer assay device designed to detect analyte binding to a fiber-optic end surface. Analyte detection is based on a change in the thickness at the end surface of the optical fiber resulting from the binding of analyte molecules to the surface, with greater amount of analyte producing a greater thickness-related change in the interference signal. The change in interference signal is due to a phase shift between light reflected from the end of the fiber and from the binding layer carried on the fiber end, as illustrated particularly in FIGS. 7a and 7b of the '453 patent. The device is simple to operate and provides a rapid assay method for analyte detection.
Ideally, an interferometer assay device will yield readily observable changes in spectral peak and valley (extrema) positions within the range of a conventional visible-light spectrometer, that is, in the visible light range between about 450-700 nm, such that relatively small optical thickness changes at the fiber end can be detected as significant changes in the spectral positions of interference wavelength peaks and valleys. One limitation which has been observed with the device described in the '453 patent is the absence of readily identified wavelength spectral extrema over this spectral range.
The present invention is designed to overcome this limitation, preserving the advantages of speed and simplicity of the earlier-disclosed device, but significantly enhancing sensitivity and accuracy. The present invention also provides a more convenient disposable-head format, as well as a multi-analyte array format, e.g., for gene-chip and protein-chip applications.